By Maddy Shah Scott, Sea Trust summer Intern 2025
For many, seaweed is what its name suggests; a weed that clogs up beaches and attracts flies. What many people don’t know is that seaweed is an unsung hero, a nutritional powerhouse and a climate-change fighter. Seaweed forests sustain high levels of biodiversity and act as nursery, feeding ground and shelter for all forms of marine life. Seaweed is also sustainable and carbon-negative and also has the power to transform and unite communities around the world. It’s time to celebrate seaweed and give it the attention it deserves.
Seaweed is the name given to marine algae and plants that grow in our oceans and there are over 10,000 species worldwide, with over 650 of these found within the UK. Just like terrestrial plants, seaweed can appear in all forms; from microscopic phytoplankton to towering kelp forests (https://oceanservice.noaa.gov/facts/seaweed.html), and just like on land, different seaweeds can harbour different ecosystems giving a whole range of benefits to the ocean and planet.
So what are the benefits? For starters, seaweed is a superfood. It’s packed full of antioxidants, vitamins and minerals, as well as being a pretty good source of iodine, which helps with pregnancy and thyroid issues. In east Asia, seaweed has been a key component of people’s diet for hundreds of years. So much so, that humans have acquired some seaweed digesting genes from fish to help aid digestion of seaweed and absorb as many nutrients as possible. (https:// www.science.org/content/article/your-gut-harbors-genes-stolen-sea-life)!
More importantly, seaweed can act as a carbon-sink, absorbing carbon dioxide from the atmosphere and helping us fight the battle against climate change. It can also help protect against the devastating effects of humans on marine ecosystems. This includes absorbing harmful run off from agriculture. Run off is the water that flows through farmland and carries harmful nutrients such as nitrogen. In excess quantities these can cause algal blooms and eutrophication, depleting the water of oxygen and starving marine organisms. Thriving seaweed populations can reduce concentrations of these harmful nutrients to promote sustainable and healthy marine ecosystems.
Kelp is a particularly cool species of seaweed. Kelp species grow in shallow coastal waters along nearly one-third of the worlds coastlines and act as super carbon absorbers, rivalling tropical rainforests in the amount of biomass that they produce. The UK has the highest diversity of kelp in Europe, however this diversity and abundance is decreasing. They can also act as storm buffers, and ecosystem engineers, creating habitat through their structure.
Scientists in the US are researching how kelp could help to remove CO2 from the atmosphere. Kelp grown on seaweed farms across the open ocean would be sunk thousands of metres to the bottom of the ocean floor, trapping CO2 for hundreds of years.
This method would bypass the need for freshwater or land, with the kelp turning CO2 into biomass as it grows.
Given the huge amounts of benefits that seaweed can bring, how can we use it sustainably to support both humans and ecosystems?
First of all, seaweed could be an excellent solution to help increase food security; it requires minimal space within expansive ocean landscapes and can double up as a carbon sequestrator. It’s fast growth means it can easily be replenished, keeping marine ecosystems alive and healthy. It’s benefits extend beyond humans; it’s a nutritious livestock feed and has been shown to actually reduce methane emissions from cows (source). It can act as a natural fertiliser, resuming the concentrations of harmful chemicals. There is even promise of seaweed being turned into a sustainable plastic.
For seaweed cultivation to continue to thrive, it must be sustainable and we must be able to replace what we have taken. For seaweed, this may look like keeping farming small, local and community-based farms with plocally sold products.
This is exactly what Car y Mor are doing. Based in St David’s, they are the first regenerative ocean farm in Wales. Their ethos is focused around cynefinoedd; a belief that nature and people should live in symbiosis. Their aim is to improve the coastal environment through seaweed and shellfish farming, whilst also creating community and trying to regenerate the once thriving fishing industry. By growing seaweed in once barren oceans, its encouraging marine life to thrive. Car y Mor highlights how seaweeds impacts are far reaching.
Due to the success of seaweed farms in small and community-based areas, seaweed plays an important role for small coastal communities around the world. Seadling is a Borneo based seaweed biotech company that offers technical services, training, and materials to farming communities to improve the quality and productivity of their farms, and guaranteed buy-back of their harvests. By working with and empowering local farmers, it produces an opportunity for scaling up within the industry whilst still remaining sustainable and helping farmers to become more resilient.